Communications services and topologies between ground control centers and associated Low Earth Orbit (LEO satellite or spacecraft segments/elements may typically be implemented in two basic fashions. One implementation uses Direct Down-Links (DDLs) between a LEO space terminal and ground terminals, such as Air Force Satellite Central Network (AFSCN) or a variety of commercial ground terminal services. Another implementation may include commercial or government owned and operated Geostationary Earth Orbiting (GEO) relays, such as the Tracking and Data Relay Satellite System (TDRSS), Milstar or other GEO based commercial satellites. Direct to ground links for LEO spacecraft's require proliferation and multiple ground terminals to increase service access and intervals, protocols and formats, with service intervals limited to short contact times with specialized links. Use of GEO relay systems, face other operational resource constraints affecting scheduling, prioritization, service acknowledgement, high use costs and sophisticated spacecraft communication terminals to provide link closure.
Inherent characteristic of many of today's LEO space systems and their communications paths are coupling of command forward paths with return wideband mission data paths. The operational and functional mission nature of many of these LEO systems is optimized when tasking is separate from mission data return, for example, when a mission event is tasked or initiated, it is not often conducive to when the data is needed by ground mission data processing centers. Therefore, decoupling forward and return paths is not only desirable, but very advantageous when considering responsiveness to adhoc spacecraft tasking along with increased cost effectiveness, especially where wideband GEO relay scheduling is extremely costly and constrained.